Date: Fri, 5 Apr 2013 07:09:24 -0400 From: Matt Miller <matt@matthewjmiller.net> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: FreeBSD Net <freebsd-net@freebsd.org>, Juan Mojica <jmojica@gmail.com> Subject: Re: panic in tcp_do_segment() Message-ID: <CAFc6gu9bmJQ-Uxv7PzspSLDyFz6zE3fV=u7HEumCh6f=YQLU2Q@mail.gmail.com> In-Reply-To: <1043692819.529554.1365114790772.JavaMail.root@erie.cs.uoguelph.ca> References: <1043692819.529554.1365114790772.JavaMail.root@erie.cs.uoguelph.ca>
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Hey Rick,
I believe Juan and I have root caused this crash recently. The t_state =
0x1, TCPS_LISTEN, in the link provided at the time of the assertion.
In tcp_input(), if we're in TCPS_LISTEN, SO_ACCEPTCONN should be set on the
socket and we should never enter tcp_do_segment() for this state. I think
if you look in your corefile, you'll see the socket *doesn't* have this
flag set in your case.
1043 /*
1044 * When the socket is accepting connections (the INPCB is in
LISTEN
1045 * state) we look into the SYN cache if this is a new
connection
1046 * attempt or the completion of a previous one. Because listen
1047 * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock
will be
1048 * held in this case.
1049 */
1050 if (so->so_options & SO_ACCEPTCONN) {
1051 struct in_conninfo inc;
1052
1053 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting
but "
1054 "tp not listening", __func__));
...
1356 syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
1357 /*
1358 * Entry added to syncache and mbuf consumed.
1359 * Everything already unlocked by syncache_add().
1360 */
1361 INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1362 return;
1363 }
...
1384 /*
1385 * Segment belongs to a connection in SYN_SENT, ESTABLISHED or
later
1386 * state. tcp_do_segment() always consumes the mbuf chain,
unlocks
1387 * the inpcb, and unlocks pcbinfo.
1388 */
1389 tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos,
ti_locked);
I think this has to do with this patch in soclose() where SO_ACCEPTCONN is
being turned off in soclose(). I suspect if you look at the other threads
in your corefile, you'll see one at this point in soclose() operating on
the same socket as the one in the tcp_do_segment() thread.
http://svnweb.freebsd.org/base?view=revision&revision=243627
817 /*
818 * Prevent new additions to the accept queues due
819 * to ACCEPT_LOCK races while we are draining them.
820 */
821 so->so_options &= ~SO_ACCEPTCONN;
822 while ((sp = TAILQ_FIRST(&so->so_incomp)) != NULL) {
823 TAILQ_REMOVE(&so->so_incomp, sp, so_list);
824 so->so_incqlen--;
825 sp->so_qstate &= ~SQ_INCOMP;
826 sp->so_head = NULL;
827 ACCEPT_UNLOCK();
828 soabort(sp);
829 ACCEPT_LOCK();
830 }
Juan had evaluated this code path and it seemed safe to just drop the
packet in this case:
+ /*
+ * In closing down the socket, the SO_ACCEPTCONN flag is removed to
+ * prevent new connections from being established. This means that
+ * any frames in that were in the midst of being processed could
+ * make it here. Need to just drop the frame.
+ */
+ if (TCPS_LISTEN == tp->t_state) {
+ TCPSTAT_INC(tcps_rcvwhileclosing);
+ goto drop;
+ }
KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
__func__));
Or, if there's someone more familiar with the locking in these paths, they
may be able to come up with a way to restructure the locks and logic to
close this window.
-Matt
On Thu, Apr 4, 2013 at 6:33 PM, Rick Macklem <rmacklem@uoguelph.ca> wrote:
> Hi,
>
> When pho@ was doing some NFS testing, he got the
> following crash, which I can't figure out. (As far
> as I can see, INP_WLOCK() is always held when
> tp->t_state = TCPS_CLOSED and it is held from before
> the test for TCPS_CLOSED in tcp_input() up until
> the tcp_do_segment() call. As such, I don't see how
> tp->t_state can be TCPS_CLOSED, but that seems to
> be what causes the panic?)
>
> The "umount -f" will result in:
> soshutdown(so, SHUT_WR);
> soclose(so);
> being done by the krpc on the socket.
>
> Anyone have any ideas on this?
> pho@ wrote:
> > I continued running the NFS tests and got this "panic: tcp_do_segment:
> > TCPS_LISTEN". It's the second time I get this panic with the same test
> > scenario, so it seems to be reproducible. The scenario is "umount -f"
> > of a mount point that is very active.
> >
> > http://people.freebsd.org/~pho/stress/log/kostik555.txt
>
> Thanks in advance for any help, rick
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